You could just bury like a half inch with spines or I’ve heard of people, who have been doin this longer than I have, shave off an inch of the spines at the bottom. So it’s easier to place in the ground. Cut/slice off all the red. You’ll have to let it callus over for another week, but it’ll be sturdier in the mix. Roots will come out if you shave the lower part off or not. It’s just about if your worried if it’s gonna wobble out of it’s pot or not. The little ring pieces I would just set on top of soil/mix. No water or harsh sun till roots form. A spot protected from summer rains, but good strong filtered light. I’d say a month maybe a little longer you should have roots. Just leave it be. When roots come you can water and acclimate to stronger sun. I have a couple Mammillaria that are ground crawlers. You’re not the only one that has kept trying to prop up a crawler;). You can kinda tell which ones are gonna crawl even before they do. They have a look to them. Now that I see yours up close don’t think it’s a backebergiana, but still definitely a Mammillaria;). Some people plant them upside down to keep them from crawling on the ground. Pics from the Google.

cactusmcharris I'm pretty sure, as you say, Notocactus. Cannot remember the flowers' colours. The bed was started on 2003 and the photos end 2006. First dig a hole and you end up with and my favourite, Echinocereus pentalophus It no longer exists, as when I sold the house, the first thing the new owners did was remove EVERY single feature and plant, and replaced with turf. I got great pleasure and enjoyment from it. Fof

Ya this cactus is etiolated. I‘ve been trying figure of what it could be. At first glance I thought it was the mini version of Austrocylindropuntia subulata, but I actually think it’s an etiolated Mammillaria. The tubercles are too prominent to be my first thought. Plus the spines look more Mammillaria imo, and it’s missing the leaves that the mini A. subulata has. Has it ever flowered?

Rebutia albiflora which is a subspecies of Rebutia pulvinosa. This makes me very 😀 to know you got this from Lowe’s. I love Rebutias and I get excited to see different species hitting the big box stores. I’ve never seen albiflora in the bbs. I find Rebutias like a little more water than other cactus during the growing season. Of course the mix needs to dry out, but once mix is dry water. I’ve had a couple Rebutia die from dried up roots because they didn’t get enough water during their growth period.